The present invention relates to electronic communication systems, and more particularly to a contention resolution scheme for an ad-hoc radio channel that supports varying quality of service requirements.
In the last decades, progress in radio and VLSI technology has enabled widespread adoption of radio communication in consumer applications. Portable electronic devices, such as mobile telephones, can now be produced having acceptable cost, size, and power consumption.
Presently, the primary focus of wireless communication technology is on voice communication. This focus will likely expand in the near future to provide inexpensive radio equipment which can be easily integrated into mobile and stationary devices. For instance, radio communication can be used to create wireless data links, thereby reducing the need for cables to connect electronic devices.
Traffic flow in data communications can be highly asymmetric. Data communication applications like downloading web pages and sending e-mail require greater bandwidth in one direction than in the opposite direction. For example, a typical user interaction with the World Wide Web is characterized by relatively low “upstream” bandwidth requirements and relatively high “downstream” bandwidth requirements.
Digital radio systems deployed for cellular phone service originally employed symmetric air interfaces, typically using a Time Division Duplex (TDD) access channel. A symmetric air interface was appropriate for voice services, which accounted for most cellular phone traffic, because traffic flows in voice service are substantially symmetric. In the cordless phone system DECT, additional flexibility was obtained since slots in a frame could be allocated more freely in downlink or uplink direction. However, DECT is based on a hierarchical network structure in which base stations support control and traffic channels based on slots, frames and multiframes.
Recently, a radio interface referred to as Bluetooth was introduced to provide wireless, ad hoc networking between mobile phones, laptop computers, headsets, PDAs, and other electronic devices. Some of the implementation details of Bluetooth are disclosed in this application, while a detailed description of the Bluetooth system can be found in “BLUETOOTH—The universal radio interface for ad hoc, wireless connectivity,” by J. C. Haartsen, Ericsson Review No. 3, 1998. Further information about the Bluetooth interface is available on the Official Bluetooth Website on the World Wide Web at http://www.bluetooth.org.
Radio communication systems for personal use differ significantly from radio systems like the public mobile phone network. Public mobile phone networks use a licensed band which is fully controlled by the network operator and provides a substantially interference-free channel. By contrast, personal radio communication equipment operates in an unlicensed spectral band and must contend with uncontrolled interference. One such band is the globally-available ISM (Industrial, Scientific, and Medical) band at 2.45 GHz. The band provides 83.5 MHz of radio spectrum. Since the ISM band is open to anyone, radio systems operating in this band must cope with unpredictable sources of interference, such as baby monitors, garage door openers, cordless phones, and microwave ovens. Interference can be avoided using an adaptive scheme that seeks out an unused part of the spectrum. Alternatively, interference can be suppressed by means of spectrum spreading. In the U.S., radios operating in the 2.45 GHz ISM band are required to apply spectrum-spreading techniques if their transmitted power levels exceed about 0 dBm.
Bluetooth radios use a frequency-hop/time-division-duplex (FH/TDD), spread spectrum channel access scheme. In the United States and in most European countries, Bluetooth radios utilize 79 RF channels spaced 1 MHz apart in the 83.5 MHz ISM band. During a connection, radio transceivers “hop” from one frequency band to another in a pseudo-random fashion. The frequency hopping sequence is determined by the device address of a Bluetooth unit. The time dimension is divided into slots of 625 μs, resulting in a nominal hop rate of 1600 hops/second. Further, slots are used alternately for transmitting and receiving, resulting in a TDD scheme. These features allow for low-cost, low-power, narrowband transceivers with strong immunity to interference.
One application for Bluetooth-enabled communication units is the replacement of cables that connect computing or communication devices, such as computers, printers, mobile terminals, and the like. To replace cables, the communication channel must be sufficiently flexible to support both symmetric and asymmetric traffic flows and synchronous and asynchronous clocking schemes. Bluetooth radios can provide this flexibility because the communication channel lacks a multi-slot frame structure.
To provide a high degree of data integrity, schemes may be implemented to retransmit data packets that have been received incorrectly by the recipient. Commonly assigned U.S. Provisional Application No. 60/180,095 describes an Automatic Retransmission Query (ARQ) proposal useful in a point-to-point transmission protocol based on a ping-pong channel access scheme. Further, commonly assigned U.S. Provisional Application No. 60/226,965 describes assigning recovery slots to communication units in a ping-pong channel access scheme. Provisional Application Nos. 60/180,095 and 60/226,965 are incorporated by reference in their entirety.
There remains a need in the art for channel access schemes useful in peer-to-peer communications that provide a highly flexible and reliable allocation of channel resources. Further there is a need in the art for a channel access scheme that accommodates varying Quality of Service (QoS) requirements.